Undetected or delayed evaluation of a bleeding patient which sometimes occurs during and after surgery is extremely dangerous and may cascade into hemorrhagic shock and result in irreversible or delayed cellular and organ damage and death. In view of this serious problem, it would be desirable if a system and method were available with the ability to continuously and non-invasively detect changes in central blood volume. Such a system would better enable early medical management of patients at high risk for acute blood loss in surgical, post-operative and trauma care settings. National average rates reported in 2011 Patient Safety Indicators (PSI's), categorized as post-operative hemorrhaging or hematoma, were trending at only 3.40 per 1,000 (0.34%) as reported via the Agency for Healthcare Research and Quality (AHRQ). However, clinical data of “high risk” surgical procedures have reported up to 11% postoperative bleeding.4 Each year in the USA more than 640,00 patients undergo open heart surgery and 0.3% to 11% (19,000 to 70,000) patients develop excessive bleeding postoperatively. About 5% percent of these open heart patients require re-exploration and revisions for bleeding. In the emergency setting, hemorrhage is responsible for over 40% of deaths within the first 24 hours after a traumatic injury.
Current methods for non-invasive monitoring of blood volume loss include vital signs monitoring of heart rate, blood pressure, respiration and oxygen saturation. This “vital signs” approach has not been shown to reliably detect small amounts of acute blood loss1,2,3. Invasive methods include central venous and arterial catheters designed to monitor hemodynamic status centrally (e.g. swan-ganz, wedge pressure measurements) but can create insertion complications such as perforations in the vasculature, pneumothorax, arrhythmias, thrombosis and infection. While invasive central monitoring may provide extremely accurate information, applications to trauma and postoperative settings are limited. The early detection and accurate evaluation of blood volume is clinically documented as having a direct influence on improving patient outcomes5,6. Data supports the need for blood volume monitoring of patients in the intraoperative, postoperative and trauma settings. Through early detection of acute and progressive blood loss, clinicians may be able to reduce incidences of morbidity and mortality associated with hemorrhagic shock while also reducing the cost of patient care. The study of non-invasive techniques for detecting early blood loss is again emerging in modern literature; however, at this time no such device is available commercially7,8.